1. Field of the Invention
This invention relates to systems for discovering polymerization catalysts, and more particularly, to methods, materials, and devices for making and screening combinatorial libraries to identify polymerization catalysts. In particular, the invention relates to a screening method that identifies catalysts that can successfully polymerize—and preferably copolymerize—olefin monomers.
2. Discussion
The present invention relates to rapidly synthesizing and identifying catalysts that can polymerize and co-polymerize a variety of olefin monomers. Ethylene is perhaps the most widely polymerized olefin, and catalysts for producing the most common variations of polyethylene, such as “low density” (LDPE), “high density” (HDPE), and “linear low density” (LLDPE) polyethylene are generally well known. As is also well known, LDPE and LLDPE are copolymers of ethylene with another monomer, such as 1-butene, 1-hexane or 1-octene.
As known to those familiar with olefin polymers, however, catalyzing the polymerization of larger olefins is difficult, and catalyzing the co-polymerization of different olefins is even more difficult, particularly when seeking a resulting copolymer with a desired set of properties. Although the task of identifying and synthesizing appropriate copolymer catalysts has been approached with some logic, the large number of candidate compounds has forced a relatively slow pace upon the development of satisfactory catalysts.
The slow pace of discovery is due, in part, to the time and expense of synthesizing and testing catalysts using conventional techniques. In traditional material science, researchers synthesize a candidate catalyst that they test or screen to decide whether it warrants further study. Combinatorial chemistry is one approach for accelerating the discovery of new polymerization catalysts. In general, combinatorial chemistry refers to the concurrent synthesis and/or testing of relatively large numbers of compounds and stands in some contrast to more traditional methods in which smaller numbers of compounds are synthesized or tested in sequential, one-by-one fashion. See, for example, U.S. Pat. No. 6,030,917 which is incorporated entirely herein by reference. It is a powerful research strategy when used to discover materials whose properties depend on many factors. Researchers in the pharmaceutical industry have successfully used such techniques to dramatically increase the speed of drug discovery. Material scientists have employed combinatorial methods to develop novel high temperature superconductors, magnetoresistive materials, phosphors, and catalysts. See, Borman, Combinatorial Chemistry Redefining the Scientific Method, Chemical & Engineering News, Vol. 78, No. 20, 53–65; and Dogani, Materials a la Combi, id at 6–68.
Currently, some of the high throughput screens that are used to seek reactive catalysts from a group of potential catalysts analyze the supposed polymerization reaction while the reaction is occurring, such as by measuring a heat of reaction with in an infrared screen. See WO 97/32208, which is incorporated entirely herein by reference. However, such high throughput screens require reaction monitoring equipment (such as an IR camera) that may be expensive and not generally robust, yet sensitive enough for an industrial research program.
Also, some of these techniques monitor a secondary characteristic of a chemical reaction (e.g., heat of reaction as noted above) rather than the properties of the end product (e.g., the physical and chemical properties of a desired copolymer). Although such secondary information can be useful, in other situations, primary information about the product may be more valuable, and in some cases, quite necessary. For example, IR detection of heat of reaction of ethylene with a catalyst does not tell one whether, for example, butene or polyethylene is being prepared.
Other existing high throughput screens are useful for measuring properties of the resulting polymers made from the synthesis of a combinatorial library. See, for example, U.S. patent applications Ser. Nos. 09/285,363; 09/285,333; 09/285,335; or 09/285,392; each of which was filed on Apr. 2, 1999, and each of which is incorporated herein by reference (and a version of which published as WO 99/51980, which is also incorporated herein by reference).
In these methods, the potential polymerization catalyst is tested using one or more monomer(s) that the catalyst will hopefully polymerize. However, some monomers are difficult to handle in a combinatorial research program that uses automated equipment. As recognized by those familiar with combinatorial techniques, the availability of automated equipment that can handle large numbers of samples (usually small samples) in relatively rapid fashion provides the capability for carrying out combinatorial techniques. Stated differently, compounds that cannot be handled using automated equipment are harder to evaluate using combinatorial techniques.
For example, the polyolefin market in the U.S. alone has been estimated at about 60 billion pounds in recent years. Although some of this market is made up of larger olefin polymers (e.g., about 6 billion pounds per year of polystyrene), the majority is made up of smaller monomer polymerization; e.g., the various types of polyethylene referred to above, as well as polypropylene. Although catalysts that will polymerize olefins may have similar properties, those catalyzing properties can and do differ among the various olefins. Thus, as a first evaluation, catalysts should be identified that will homopolymerize any given monomer efficiently. Because copolymers are so important, however, catalysts also need to be identified that will copolymerize different monomers, and do so in desired manners and proportions. For example, a catalyst that copolymerizes two olefins in a manner such that the proportion of one overwhelms the other is not helpful if a more balanced proportion of each monomer is desired or necessary.
In this regard, ethylene reacts with many potential polymerization catalysts. Thus, testing ethylene may provide little or no information about catalysts that will successfully polymerize or copolymerize other monomers, particularly the larger monomers. In addition, monitoring secondary information for ethylene will not provide information regarding whether butenes or oligomers are being made or of a polymer of a desired molecular weight is being prepared.
Thus, a new method of screening catalysts for polymerization activity is needed, where such monomers can be easily handled in a combinatorial research methodology, and a screen of the product properties is need. The needed method should also be fast, given the vast number of possible catalysts.